A gasket is an article which is clamped between adjacent faces and acts as a static seal. Depending upon its particular application, a gasket may be required to resist extremely high and/or low temperatures, elevated pressures and/or vacuum, thermal expansion, and various chemicals. The use of gaskets in internal combustion engines is very prevalent. For example, in internal combustion engines gaskets are used to create a seal to keep engine fluids, such as oils, fuels, coolants, within the engine and to keep outside dirt and other contaminants from entering the engine. Gaskets of desired sizes and shapes are often made by stamping them out of gasketing paper.
Gasketing paper is often made by the beater-addition process. The beater-addition process is described in U.S. Pat. No. 2,759,813. In the beater addition process, a slurry of at least one fiber in water is mixed with a rubber latex. This slurry also often contains one or more fillers. The latex in the slurry is precipitated to form a furnish composition. The furnish is then processed into sheet by removing excess water via a cylinder machine, a fourdrinier, or similar processing equipment. Additional water is pressed out of the sheet with vacuum generally being applied to enhance evaporation. The sheet is then further dried in drying ovens or on steam cans. The dried sheet is then generally calendared into gasketing paper having the desired density. Gaskets of the desired shape can then be stamped out of the gasketing paper and cured.
The gasketing paper typically contains curatives, such as amines, sulfur and/or zinc compounds, which are needed to cure conventional rubbers therein. The beater addition process has been criticized from an environmental standpoint because these curatives are released into the environment through the effluent from the process. It would accordingly be desirable to develop a latex of a rubber which can be cured without the need to utilize conventional curatives. Such a rubber composition is disclosed in U.S. Pat. No. 4,983,684, filed on Feb. 27, 1989. Such rubber compositions can be cured (crosslinked) by heating without the need for conventional curatives. U.S. Pat. No. 4,983,684 discloses three types of rubber compositions which can be cured without utilizing conventional curatives. The first type of rubber composition described is comprised of (1) at least one rubber having pendant block isocyanate groups bound thereto; and (2) at least one compound which contains at least 2 Zerewitinoff active hydrogens. The second type of rubber composition is comprised of (1) at least one rubber having Zerewitinoff active hydrogens bound thereto; and (2) at least one compound having at least two block isocyanate groups bound thereto. The third type of rubber composition disclosed is comprised of polymer chains having (1) pendant blocked isocyanate groups bound thereto; and (2) Zerewitinoff active hydrogens bound thereto. It is highly preferred for the latices utilized in practicing this invention to contain this "self-curing" type of rubber which has both pendant blocked isocyanate groups and groups containing active Zerewitinoff hydrogen.